The present invention relates to a fuel-cell system preferably mounted to various moving body such as an automobile and a control method of the fuel-cell system. More particularly, the invention relates to a fuel-cell system for a moving body that can idle the moving body which is effective in terms of re-acceleration and fuel economy, and relates to a control method of the fuel-cell system.
The fuel-cell system of this kind is an apparatus for directly converting energy having the fuel into electric energy. The fuel-cell system supplies hydrogen-rich gas toward a cathode (fuel pole) of a pair of poles provided such as to sandwich an electrolyte film, and supplies gas including oxygen toward the other pole, i.e., an anode (oxidizer pole). The fuel-cell system taken out electric energy from the poles utilizing the following electrical reaction generated on surfaces of the pair of poles at the side of the electrolyte film:
Anode reaction: H2xe2x86x922H++2exe2x88x92
Cathode reaction:2H++2exe2x88x92+(1/2) O2xe2x86x92H2O
As a apparatus for generating the hydrogen-rich gas which will become superconductive fuel, a reforming reactor reforming methanol into fuel gas including large amount of hydrogen is used. As an apparatus for generating oxidizer including oxygen, a compressor for taking in air to produce compressed air is used. The compressed air from the compressor is cooled by an aftercooler or the like and then, the air is supplied to the anode of the fuel-cell, on one hand, the methanol gas is sent from a fuel tank to a reforming reactor, and the reformed hydrogen-rich gas is supplied to the cathode of the fuel-cell.
As compared with an electric automobile using a secondary battery, the fuel-cell system is advantageous in terms of travelable distance, maintenance condition of infrastructure of fuel and the like. Therefore, it is studied to employ the fuel-cell system as an electric source for driving vehicles.
As the reforming reactor, in addition to a vapor reforming type reforming reactor for vapor-reforming hydrocarbon such as methanol, there is proposed a so-called auto-thermal type reforming reactor for facilitating the vapor reforming reaction of the hydrocarbon which is an endothermic reaction utilizing heat discharged by oxidation of the hydrocarbon (e.g., see Japanese Patent Application Laid-open No.H9-315801). In the auto-thermal type reforming reactor of this kind, air (oxygen), water vapor and hydrocarbon such as methanol are mixed and flowed into a reactor charged with a copper-based catalyst, a noble metal or a VIII group metal catalyst, thereby causing the following reactions:
Partial oxidation reaction: CH3OH+1/2H2O2 xe2x86x922H2+CO2+189.5 kJ/mol
Vapor reaction: CH3OH+Oxe2x86x923H2+CO2+xe2x88x9249.5 kJ/mol
Then, a heat amount necessary for the vapor reforming reaction (endothermic reaction) using the heat generated by the partial oxidation reaction (exothermic reaction), and a small reforming reactor requiring no outside heater such as a burner can be provided.
Further, the reformed gas generated by the reforming reaction includes impurities such as small amount of non-reformed fuel gas or carbon monoxide in addition to hydrogen and carbon dioxide. If gas including such impurities such as non-reformed fuel gas and carbon monoxide is supplied to the fuel as it is, the platinum which is used regularly as electrode catalyst of fuel-cell is poisoned and there are problems that catalytic activity is lost and battery performance is lowered.
Thereupon, the reformed gas generated by the reforming reactor is allowed to pass, together with air, into a carbon monoxide removing apparatus having oxidation catalyst, thereby facilitate the oxidation reaction of carbon monoxide (CO+1/2O2xe2x86x92CO2) so that the concentration of the carbon monoxide is lowered. By providing such a carbon monoxide removing apparatus in the fuel-cell system, the cell performance is prevented from being lowered, and the hydrogen in the reformed gas is purified higher and thus, the electric power generating efficiency is enhanced.
In a fuel-cell system mounted to a moving body such as a vehicle, as a driving control method when an accelerator is closed during running, there is a method for stopping the actuation of the system by cutting the fuel supply or for driving the moving body at low load as an internal combustion engine such as a gasoline engine. As the method for driving the moving body at low load, like the idling is carried out in the internal combustion engine, it seems to be possible to throttle fuel, water and air to be supplied to the reforming reactor, or to intermittently supply fuel, water and air.
However, in the fuel-cell system mounted in the moving body, if the accelerator is closed during running, since a regenerative function acts to charge the secondary battery, electric power generation by the fuel-cell stack under this condition is basically unnecessary. However, when the secondary battery is insufficiently charged, the electric power generation is effective in some cases.
When the electric power generation by the fuel-cell stack is unnecessary, since the reforming system does not need to supply the hydrogen gas to the stack, it is preferable, in terms of fuel economy, to cut the fuel supply like the internal combustion engine such as the gasoline engine to stop the system or drive the system at a low load.
However, if the fuel-cell system is stopped, temperature of catalysts of various reactors such as the reforming reactor, the carbon monoxide removing apparatus and the combustor is gradually lowered, and when the vehicle descends a long hill and then re-accelerates such as an expressway, the catalyst temperature of each reactor becomes excessively low, and even if reaction is required by re-acceleration or the like, there is an adverse possibility that the vehicle can not react sufficiently.
When the accelerator is closed, if the reforming system is driven at low-load driving state such as an idling state of the internal combustion engine, it is possible to always keep such a temperature of each reactor that the reactor can react. However, it is difficult and not efficiency to drive the reforming system at low-load driving state. Thus, fuel is excessively consumed, and fuel economy can not be prevented from being deteriorated.
It seems to be possible to intermittently supply fuel instead of flowing gas of low flow rate as low-load driving, but if the fuel is merely supplied intermittently, it is difficult to largely reduce the fuel consumption, and if the carbon monoxide removing reactor and hydrogen gas by the combustor are not utilized, the fuel economy can not be prevented from being deteriorated.
The present invention has been accomplished in view of these problems of the prior art, and it is an object of the invention to provide a fuel-cell system for a moving body and a control method of the system capable of idling the moving body in a most effective manner in terms of fuel economy and re-acceleration when an accelerator is closed.
To achieve the above object, the present invention provides a fuel-cell system for a moving body comprising: a reforming reactor for reforming fuel to generate gas including hydrogen, a carbon monoxide removing reactor for removing carbon monoxide included in a reformed gas generated in the reforming reactor, a fuel-cell for generating electric power using the reformed gas and gas including oxygen which passed through the carbon monoxide removing reactor, a compressor for supplying the gas including oxygen to the reforming reactor, the carbon monoxide removing reactor and the fuel-cell, a running state detecting section for detecting a running state of the moving body, an accelerator opening detecting section for detecting accelerator opening of the moving body, and a control section, wherein when the control section judged that the moving body was running and the accelerator was closed based on information of the running state detecting section and the accelerator opening detecting section, the control section supplies fuel, water and gas including oxygen, or fuel and the gas including oxygen such to the reforming reactor such that minimum hydrogen required for maintaining a temperature of the reforming reactor is generated, and supplies minimum gas including oxygen required for maintaining a temperature of the carbon monoxide removing reactor to the carbon monoxide removing reactor.
In other words, the present invention provides a fuel-cell system for a moving body comprising: a reforming reactor for reforming fuel to generate gas including hydrogen, a carbon monoxide removing reactor for removing carbon monoxide included in a reformed gas generated in said reforming reactor, a fuel-cell for generating electric power using the reformed gas and gas including oxygen which passed through said carbon monoxide removing reactor, a compressor for supplying the gas including oxygen to said reforming reactor, said carbon monoxide removing reactor and said fuel-cell, a running state detecting means for detecting a running state of said moving body, an accelerator opening detecting means for detecting accelerator opening of said moving body, and a control means, wherein when said control means judged that said moving body was running and said accelerator was closed based on information of said running state detecting means and said accelerator opening detecting means, said control means supplies fuel, water and gas including oxygen, or fuel and the gas including oxygen such to said reforming reactor such that minimum hydrogen required for maintaining a temperature of said reforming reactor is generated, and supplies minimum gas including oxygen required for maintaining a temperature of said carbon monoxide removing reactor to said carbon monoxide removing reactor.
Besides, a control method of a fuel-cell system for a moving body comprising a reforming reactor for reforming fuel to generate gas including hydrogen, a carbon monoxide removing reactor for removing carbon monoxide included in a reformed gas generated in said reforming reactor, a fuel-cell for generating electric power using the reformed gas and gas including oxygen which passed through said carbon monoxide removing reactor, and a compressor for supplying the gas including oxygen to said reforming reactor, said carbon monoxide removing reactor and said fuel-cell, wherein when it is judged that said moving body was running and said accelerator was closed, fuel, water and gas including oxygen, or fuel and the gas including oxygen such is supplied to said reforming reactor such that minimum hydrogen required for maintaining a temperature of said reforming reactor is generated, and minimum gas including oxygen required for maintaining a temperature of said carbon monoxide removing reactor is supplied to said carbon monoxide removing reactor.
According to the invention, hydrogen which must be generated by the reforming reactor for maintaining the temperature is only hydrogen for warming the reforming reactor itself for the generated heat and hydrogen for causing oxidization reaction of the generated hydrogen in the carbon monoxide removing reactor. Thus, the fuel consumption is minimized. Further, since the temperature of each of the reforming reactor and the carbon monoxide removing reactor is maintained, the response at the time of re-acceleration is enhanced.